For some years, poultry houses have been constructed with a relatively low roof which comes down to a point on either side of the center a few feet above the ground. Rather than solid, permanent side walls to connect the edge of the roof and the ground, one or more curtains are provided which may be selectively raised or lowered to control the amount of natural ventilation or to be used in conjunction with forced ventilation systems. Forced ventilation systems have been used with increasing frequency as a year round system. In winter months forced ventilation prevents moisture from forming inside which normally would occur and could drip from the roof causing the floor to become damp. In such systems it is conventional for the curtains to be raised from a lowered, open position to a closed or upper position with a winch and cable device.
The normal curtain positions when using forced ventilation (several electric fans which usually are powered by 220 volt power and are mounted in the side wall of the poultry houses such as normal exhaust fans) is with one curtain closed (up) and the other only open a few inches for air intake. Thus the inside of the house has an atmospheric pressure slightly less than outside. Some poultry houses with forced ventilation systems are operated with louvers as an air intake means. In such systems both curtains are normally closed (up). This forced ventilation system, as it is called by the poultry industry, is being used more and more to produce better quality poultry with less expense and less space per bird. The system requires several large fans for each house. Some of the electrical fans are operated on electrical timers and some are controlled by thermostats using an over-ride system with the timers and thermostats. Six fans each requiring a 3/4 horse power motor would be normal for a house large enough to raise 15 to 20 thousand birds.
Such a system is quite satisfactory as far as ventilation and protection from the weather is concerned, unless a power failure occurs in the electrical circuit of the ventilating system. In such a case, without proper ventilation, the conditions within the poultry house make it extremely warm, and without proper air, the poultry can suffocate.
There has been developed at least one commercially available unit which, upon a power failure, activates a separate circuit containing a dry cell battery which heats a nichrome heater wire. A nylon cord extends from the curtain raising and holding apparatus and maintains the curtain in a closed position. The cord also passes closely adjacent the nichrome wire, so that as it heats, the cord burns through releasing the curtain raising apparatus causing the curtain to drop, thus providing natural ventilation.
There are several disadvantages to such a type of system. For example, the battery, when needed, may be in a poor condition and unable to deliver the power to perform its function. The user has no sure way of knowing if the system will perform. The dry cell being enclosed inside the unit is forgotten or neglected. If a storage battery is used it is costly and must be given regular attention to maintain it in a charged condition. Also, every time the power fails and the system is activated, the nylon cord, which is burned through, must be replaced. Furthermore, in dry conditions which frequently occur in poultry houses, there is generally substantial flammable material around, which could be dangerous with the nichrome heater wire which is heated to a temperature between 1000.degree. to 1300.degree.F.